Impact energy management method and system

ABSTRACT

An impact-absorbing protective structure comprises one or more compressible cells. Each cell is in the form of a thin-walled plastic enclosure defining an inner, fluid-filled chamber with at least one small orifice through which fluid resistively flows. Each cell includes an initially resistive mechanism that resists collapse during an initial phase of an impact and that then yields to allow the remainder of the impact to be managed by the venting of fluid through the orifice. The initially resistive mechanism may be implemented by providing the cell with semi-vertical side walls of an appropriate thickness or by combining a resiliently collapsible ring with the cell. After the initially resistive mechanism yields to the impact, the remainder of the impact is managed by the fluid venting through the orifice. The cell properties can be readily engineered to optimize the impact-absorbing response of the cell to a wide range of impact energies.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of Ser.No. 11/543,642, filed Oct. 5, 2006, which is a continuation-in-part ofUS2006/005857, filed Feb. 16, 2006. The contents of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an impact energy management methodand system. More specifically, it relates to an impact energy managementmethod and system which is designed to protect an impacted object orbody from damage due to impacts and which has properties that arereadily customized to provide optimum impact-attenuating responses overa wide range of impact energies.

2. Background Information

A. The Physics of Colliding Objects

An object in motion possesses kinetic energy (KE), which is a functionof its mass (m) and velocity (v), described by the equation:

KE=½mv ²  (1)

When that object collides with another object, the energy istransferred, imparting a Force (F). The force transmitted is a functionof two primary relationships.

First, Force (F) imparted to an object is equal to the object's mass (m)and its resulting acceleration (a), as governed by Newton's Second Lawof Motion, Force=mass×acceleration or F=ma. Acceleration (a) measuresthe object's change in velocity (Δv) over time (t) (change in velocitycan be positive or negative, therefore acceleration can represent eithera positive or negative quantity), thus Newton's Law can be re-written asfollows:

F=m((Δv)/t)  (2)

From this equation, it is apparent that one way to reduce the Forceimparted to an object of fixed mass (m) is to prolong the time (t) overwhich the object changes velocity, thus reducing its acceleration.

Second, Force (F) is a result of the distance (d) over which theobject's Energy (E) (in the form of kinetic energy) is transferred,giving the equation:

F=E/d  (3)

From this equation, it is apparent that another way to reduce the Force(F) of an impacting object with a given amount of Energy (E) is toprolong the distance (d) over which the object's Energy (E) istransferred.

A third relationship governs the effect of an imparted force. Pressure(P) describes the concentration of Force (F) over the area (A) withinwhich the Force (F) is imparted and is governed by the equation:

P=F/A  (4)

From this equation, it is apparent that the pressure (P) of an impactcan be reduced by reducing the Force (F) imparted by the impactingobject or by increasing the Area (A) over which that Force (F) isimparted.

Given the above three relationships, it is apparent that the methods toreduce the damage caused by an impacting object are to decrease thelevel of Force (F) imparted by prolonging the time (t) over which thatobject accelerates (or decelerates) or the distance (d) over whichenergy is transferred, or to increase the area (A) over which that Force(F) is spread. An ideal system would employ all three methods to reduceimpact damage.

Force is measured in Newtons (1 N=1 kg-m/s²) or pounds (lb): mass ismeasured in kilograms (kg) or pounds of mass (lb-m): and acceleration ismeasured in meters per second per second (m/s²) or feet per second persecond (ft/s²). A commonly known force is Weight (w) which measures theforce of gravity acting on an object. It is equal to the object's mass(m) multiplied by the acceleration due to gravity (g), which is 9.81m/s² or 32 ft/s². When comparing forces that act on objects of the sameor similar mass (m), it is common to express them in terms of units ofacceleration rather than units of force (recall F=ma). In such cases,acceleration is often expressed as multiples of the acceleration ofgravity, or in “g′s”. Thus, an object can be said to have experienced an“80-g” force, or a force equal to 80 times the force of gravity. Ingeneral, it can be assumed that higher forces are more damaging to anobject than lower forces.

In any activity in which two objects are likely to collide, it is commonpractice to utilize protective structures or materials designed tomanage the energy of the collision and to minimize the damage to theimpacted object caused by the collision. A common method of testing theefficacy of such protective systems is to impart a known Force (F) toone side of the protective structure or material and to measure theforce transmitted through the system to the other side. Often this isaccomplished with a “drop test.” In this type of test, an impactingobject is dropped (or mechanically accelerated) from a given height ontoa fixed surface, which is adapted to register the force imparted to itby the impacting object. It is typical for the impacted surface to be asteel plate, beneath which is attached a “force ring,” which is capableof registering the forces delivered to the plate, and transmitting asignal representative of the forces to a data capture system, typicallya programmed computer. The combination of steel plate and force ring istermed a “force plate.” Thus a useful comparison of protective systemsinvolves placing the energy management system or material onto the forceplate, dropping an impacting mass onto the system or material, andregistering the forces transmitted through the system or material to theforce plate as a function of time.

The greater the height from which an object of fixed mass is dropped,the higher the velocity it will attain before impact, and the morekinetic energy it will possess to transfer to the impacted surface. Theforce of that impact over time is represented in a Force/Time curve,such as the curve shown in FIG. 1 of the accompanying drawing.

It is important to note that all objects with the same mass and sameimpact velocity will possess the same amount of energy. The way in whichthat energy is managed by a protective structure or material willdetermine the shape of the Force/Time curve. For a given objectimpacting with a given speed, the area under the Force/Time curve, knowas the Impulse (I), will be the same, regardless of the shape of thecurve. However, the shape of that curve is a representation of the forceprofile, which can vary significantly, depending on the energymanagement system being employed. In general, when managing impacts, thelevel of peak force attained can be considered to be the most criticalindicator of an energy management system's efficacy.

B. Foam as an Impact-Absorbing Material

One of the most common materials used to protect objects from impactforces is foam. Solid foams form an important class of lightweightcellular engineering materials, and are used in many applications whereimpacts are common, such as in athletic activities (e.g., protectiveheadgear) and automotive applications (e.g., dashboard coverings). Themost general definition of foam is a substance that contains arelatively high volume percentage of small pores, and which is formed bytrapping gas bubbles in a liquid or solid. The pores allow foam todeform elastically under impact, and the impact energy is dissipated asthe material is compressed. In general, foams decrease impact pressureby spreading forces over a wide area and by prolonging the distance andtime over which impacts occur and thus reducing the level of forcetransmitted.

While foams have been a mainstay in impact protection for decades, theyrely solely on material deformation for their energy managementcapabilities. This presents two major limitations.

First, relying on material properties severely limits the adaptabilityof the foam. Foams can be customized to respond optimally to only a veryspecific range of impact energies, either by changing the density orgeometry (thickness) of the foam, but foams are not able to adapt theirresponse to a wide range of impact energies. This can lead to a mismatchof the foam's functional capability to the impact energy, making thefoam either “too soft” or “too hard” for the impact. A foam that is toosoft (not dense enough) for an impact will compress too quickly or“bottom out” and transmit too much force to the impacted body. A foamthat is too hard (too dense) for an impact will not compress enough andwill decelerate the impacted body too quickly.

When foam becomes fully compressed under impact, it acts as a rigid bodyand loses its ability to absorb energy. The impact energy remainingafter the foam is fully compressed is transmitted directly through thefoam to the impacted body. A foam that is too soft for a given impactwill compress too quickly, which allows large forces to be delivered tothe impacted body and effectively decreases the functional distance andtime over which the impact occurs. A Force/Time curve for a foam that istoo soft for a given impact is shown in FIG. 2 of the accompanyingdrawing.

In the initial phase of impact, the foam does not slow the objectenough, and this is represented by an early, only gradually increasingline segment on the Force/Time curve of FIG. 2, from 0 to 0.075 seconds.Next, during time period from 0.075 to 0.0125 seconds, the foam quicklycompresses and packs down, at which point deceleration occurs in a shortdistance and time, shown as the spike in the curve of FIG. 2. This curvedemonstrates that the majority of the deceleration occurs in a briefperiod of time and distance, thus delivering a high peak force, which isthe most damaging to the impacted body. In addition, the potential forlocalized compression of the soft foam decreases the area over which theforce may be transmitted, therefore potentially increasing the pressureand damage of the impact. Due to potentially catastrophic consequencesof bottoming out within a small area, soft foams cannot be used insituations that may involve moderate or high energy impacts.

Conversely, a foam can also be too hard (too dense) for a given impact.If the foam is too hard, it will present too much resistance in theearly phase of the impact, and will not compress enough (will not“ride-down” enough) to prolong the distance or time of impact. It thushalts the object suddenly, represented as the sharp continuous rise to ahigh peak force in the Force/Time curve shown in FIG. 3 of the drawing.This is most evident with respect to the curve labeled “Trial 1” in FIG.3.

These dense foams function primarily to spread impact area and reducepressure to on the area, but can still lead to high forces. Anotherproblem with dense foams is the potential for high “rebound,” in whichthe foam temporarily stores impact energy in compression, thenre-delivers it upon rebound. Thus, dense foams are useful for reducingpressure of impacts, but their ability to significantly reduce peakforce is limited.

Even when foams happen to be matched to the impact (which may occur bychance, or by specific engineering of foams to meet certain veryspecific energy level standards), they still have inherent limitations.One major limitation is the inability of the foam to “ride-down” enoughto prolong the distance and time of the impact. Most foams willride-down to a maximum of 60-70% of their original height, which limitsthe distance and time over which the impact occurs, and leads to higherpeak forces. Given the limited ability to customize foams, for a givenmaterial operating at a given energy level, this presents only oneoption to further reduce peak forces. Specifically, the only way tofurther reduce peak forces is to lower the density of the foam andincrease its height or thickness. This modification can serve to lowerthe peak forces, but due to the inherent properties of foam, which causeit to become progressively denser under compression, the curve is stillhump- or bell-shaped, limiting the foam's ability to lower peak force.Further, an increased thickness of foam may be cosmetically orpractically unacceptable for certain applications, and may also increasethe bulk and weight of the energy management system to unacceptablelevels.

Given the properties of foam, once it is manufactured, it will have acertain energy level at which it performs “optimally,” but thisperformance still leaves great room for improvement, and outside of itsoptimal range the foam's function will be even worse, either beingpotentially too hard or too soft for a given impact. Thus, foam lacks anability to adapt to the potential for impacts of different energylevels. This leads to the use of foams designed simply to perform bestat a certain standard, or designed to prevent only the most criticalforms of damage, but leaving other forms of damage poorly addressed.FIG. 4 of the drawing includes two Force/Time curves for a given foamgenerated in response to two different impact energies. As is apparentfrom FIG. 4, the foam's performance declines with increased impactenergy.

The second major limitation of foam is that all foams will show declinein function after repeated impacts. Some common foams, such as expandedpolystyrene (EPS), are designed for only a single impact. Other foams,even though designed to be “multi-impact,” will also decline in functionafter repeated impacts. This lack of durability can present practical aswell as safety limitations with the use of foams. FIG. 5 of the drawingincludes a series of Force/Time curves for successive impacts to a“multi-impact” foam illustrating the decline in the foam's performancewith repeated impacts.

In summary, the problems associated with foam as an impact-absorbingmaterial include:

(a) limited adaptability;

(b) non-optimal impact energy management;

(c) tradeoff between energy absorbing ability and amount of materialused; and

(d) poor durability.

While we have specifically focused on the limitations of foams, thoseskilled in the art will appreciate that other mechanisms of energymanagement may be employed, and that they may also be subject to thesame or similar functional limitations as foam.

There is thus a need in the art of impact energy management for a novelsystem capable of addressing the limitations of foams and otherconventional energy management systems.

SUMMARY OF THE INVENTION

In accordance with the present invention, a novel impact energymanagement method and system is provided which is designed to addressthe limitations of foam and other conventional energy management systemsas discussed above.

In accordance with the present invention, an impact energy managementmethod is provided for protecting a body from damage due to impactsimparted to the body which comprises the steps of:

(a) placing a protective structure over a portion of the body to beprotected, the protective structure being capable of reducing forces ofan impact that are transferred through it to the body;

(b) providing the protective structure with a first impact-absorbingmechanism that resists yielding in response to an initial phase of theimpact and that yields to the impact after the initial phase of theimpact; and

(c) providing the protective structure with a second impact-absorbingmechanism that operates after the initial phase of the impact such thatthe forces of the impact that are transferred to the body remainsubstantially constant throughout the remainder of the impact.

In accordance with an illustrative embodiment the invention, theprotective structure comprises one or more impact-absorbing compressiblecells, either alone or in combination with other impact-absorbingmaterials and/or layers. Each cell is in the form of a thin-walledenclosure of a thermoplastic material defining an inner, fluid-filledchamber with at least one orifice. Each cell is adapted to resist animpact applied to it during the initial or early phase of the impact,and then deliberately yield to permit the fluid in the inner chamber ofthe cell to manage the remainder of the impact by venting fluid throughthe orifice. Each cell is further adapted to return to its originalshape, and the orifice is adapted to permit rapid refill of the fluid inthe inner chamber of the cell, so that after the impact, the cell isready to accept and attenuate additional impacts.

In the preferred embodiment of the invention, the cell has asubstantially round, symmetrical disk shape and is provided with sidewalls that are semi-vertically oriented and of a thickness such thatthey resist collapse during the initial or early phase of an impact onthe cell and such that they later buckle outwardly to allow the fluid inthe cell to manage the remainder of the impact by venting through theorifice. By carefully selecting the properties of the cell, such as thematerial from which the cell is fabricated, the thickness of its walls,the geometry of the cell, the fluid content of the cell and the size,configuration, location and number of venting orifices, the cell can becustomized to provide an optimal response to impacts over a wide rangeof impact energies.

Various alternative embodiments of protective compressible cellstructures are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be better understood by those skilled in the art from thefollowing detailed description of illustrative embodiments taken inconjunction with the accompanying drawings in which:

FIG. 1 is a typical Force/Time curve for an impact-absorbing material,showing the force transmitted by the material as a function of time;

FIG. 2 is a Force/Time curve for a foam material that is too “soft” forthe impact applied to the foam;

FIG. 3 is a series of Force/Time curves for a foam material that is too“hard” for a given impact (i.e., Trial 1) applied to the foam;

FIG. 4 shows two Force/Time curves for a given foam illustrating thechange in the performance of the foam in response to different impactenergies;

FIG. 5 is a series of Force/Time curves for a foam material illustratingthe decline in the performance of the foam as a result of repeatedimpacts;

FIG. 6 is a side view, partly in section, of a compressible cellembodied in accordance with the invention;

FIG. 7 is a top view of the cell of FIG. 6, illustrating its generallyround, symmetrical shape and configuration;

FIG. 8 is a Force/Time curve for a cell such as that shown in FIG. 6,illustrating how the cell can be customized to produce a nearlytrapezoidal and flattened force response;

FIG. 9 shows two Force/Time curves for a cell such as that shown in FIG.6, illustrating the response of the cell to two different impactenergies;

FIG. 10 shows a Force/Time curve for a compressible cell having a saucershape, with no initially resistive mechanism;

FIG. 11 shows a Force/Time curve for a compressible cell havingbellows-like side walls, again with no initially resistive mechanism;

FIG. 12 is a schematic illustration showing a cross section andgeometric details of a preferred cell embodied in accordance with theinvention;

FIG. 13 is a schematic illustration showing cross sections of other cellshapes potentially suitable for the invention;

FIG. 14 is a side view, partly in section, of a second embodiment of theinvention in which the initially resistive mechanism comprises aresiliently collapsible ring positioned inside the cell;

FIG. 15 is a side view, partly in section, of a third embodiment of theinvention in which a cell such as that shown in FIG. 6 is combined withfoam base plate to enhance the shock-absorbing response and durabilityof the cell;

FIG. 16 is a side view of a fourth embodiment of the invention in whicha cell such as that shown in FIG. 6 is combined with a second cell ofsimilar construction;

FIG. 17 shows a plurality of cells such as the cells shown in FIG. 6,14, 15 or 16 arranged side-by-side to form a middle layer of amultilayered protective structure having an outer shell and an innerlayer, and

FIG. 18 is a sectional view of a fifth embodiment of the invention inwhich the cell has inverted side walls.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A compressible, impact-absorbing compressible cell 10 embodied inaccordance with the invention is shown in FIGS. 6 and 7 of the drawing.

In the illustrative embodiment of FIGS. 6 and 7, the cell 10 is madefrom a thermoplastic material, such as a thermoplastic elastomer (TPE)material, formed into a thin-walled, hollow enclosure 12 with a top wall14 a and a bottom wall 14 b and an orifice 16 through its bottom wall 14b. The side walls 18 of the cell 10 are oriented semi-vertically, suchthat they provide an initial resistance to an impact on the cell 10, butthen strategically buckle outwardly to allow the fluid in the cell 10,in this case air, to manage the remainder of the impact by ventingthrough the orifice 16, as indicated by the air flow arrow 20. Theresilient properties of the thermoplastic material from which the cell10 is fabricated, coupled with the refill of air through the orifice 16,allow the cell 10 to quickly return to its original shape after impact.

FIG. 7 is a top view of the cell 10, showing its generally round andsymmetrical disk shape and configuration. This generally symmetricalshape allows the cell to respond consistently regardless of where on thecell 10 the impact is applied and regardless of the angle of the impactrelative to the cell 10.

The basic concept of the cell 10 specifically addresses the limitationsof conventional foams and other similar energy management materials andstructures, and is different from other air systems previously employedin energy management systems. First, the cell 10 provides multiplecustomization options, including selection and alteration of theproperties of the thermoplastic material from which it is fabricated,the thickness of its walls, the geometry of the cell, the fluid contentof the cell, and the size, configuration, location and number of ventingorifice(s). By carefully selecting and adjusting these properties, incoordination with one another, the function of the cell 10 can becustomized, allowing for a more robust functional range than hasheretofore been possible with conventional foams and other systems.Careful calibration of these several properties will allow those skilledin the art to determine the optimum combination based on the particularapplication to which the cell 10 is to be put.

Second, the cell 10 serves to manage impact energy in a unique way. Itwill be recalled from above that, for an object of a given mass (m)traveling at a given velocity (v), that object's Impulse, or area underits Force/Time curve, will be the same. However, the manner in which theimpact-absorbing cell 10 manages that Impulse will determine the profileof the Force/Time curve. Recall that even optimal foams will yield abell- or hump-shaped Force/Time curve. However, the cell 10 allows thesame Impulse to be managed in a different way from foam. As opposed tothe bell- or hump-shaped curve, the cell 10, due principally to itsinitially resistive mechanism, manages the Impulse such that theForce/Time curve becomes nearly trapezoidal, rising rapidly to a plateauand then, due principally to the fluid venting mechanism, displays asignificant flat portion throughout much of the remainder of the Impulsebefore it returns to zero. Thus, the cell 10 can reduce the peak forcesthat it transfers by managing the Impulse such that its Force/Time curveactually is “flattened”. An example of a flattened Force/Time curve ofthe type yielded by the cell 10 of the invention is shown in FIG. 8 ofthe drawing.

In order to manage this Impulse in such a fashion that the normallybell-shaped Force/Time curve becomes nearly trapezoidal and flattened,the above-mentioned properties of the cell 10, namely, material, wallthickness, cell geometry, fluid content and size, configuration locationand number of orifices, are selected in coordination with each other toyield the desired response. Specifically, these properties are selectedso that, in the initial part of the Impulse, the initially resistivemechanism, for example, the collapsible side walls 18 of the cell 10,serve to begin the deceleration of the object, as represented by thesteeply inclining initial portion of the Force/Time curve of FIG. 8, forthe time period from 0 to 0.005 seconds. Once the side walls 18 of thecell 10 start to collapse and buckle outwardly, the impact is managed bythe fluid venting from the cell 10 through the orifice 16, which isrepresented by the flat portion of the curve of FIG. 8, for the timeperiod from 0.005 to 0.02 seconds.

One of the major reasons the cell 10 is able to better manage impactenergy is that the fluid venting permits the cell 10 to “ride-down” to amore optimal distance than foams; in most cases, depending on theparticular wall thickness of the cell 10, it can readily compress toover 90% of its original height. This compressive ability allows theimpact to occur over greater distance and time than foams. Moreover, thefluid in the cell 10 does not become substantially more dense duringcompression, thus allowing for a more constant resistance over time anddistance, as opposed to foams which become progressively denser withcompression and lead to a spiked curve. The increased ride-down andconstant density of the cell 10 yield a flatter Force/Time curve,indicating a “softer landing” to the impacting object.

Another major benefit of the cell 10 is its ability to adapt todifferent impact energy levels. This benefit results generally from theproperties of fluids under compression. In this case, with increasedenergy of impact, the fluid in the inner chamber 12 of the cell 10becomes increasingly turbulent and does not flow as easily through theorifice 16 as compared to its flow under lower energy impacts. Thus, thefluid actually behaves as a stiffer mechanism under high impact energyas compared to its softer behavior under lower impact energy. Thisadaptation provides more optimal energy management over different impactenergy levels. An example of this adaptation of the cell 10 is shown inFIG. 9 of the drawing. FIG. 9 shows the Force/Time curves for acompressible cell such as cell 10 at two different impact energy levels;from these curves, it is apparent that the peak forces of the twoimpacts are relatively the same, despite the increased energy of impactand size of Impulse in the second curve. This adaptation provides avaluable advantage over foams, as is evident from a comparison of thecurves of FIG. 9 to the curves for a single foam at two different impactenergy levels shown in FIG. 4 of the drawing.

Finally, the cell 10 has the potential for exhibiting greater durabilitythan foams. Depending on the material chosen for the cell 10, and withthe potential for combining the cell 10 with a complementary energymanagement component, such as discussed in connection with theembodiments of FIGS. 13, 14 and 16 below, the cell 10 can exhibitconsistent impact-absorbing performance with little or no decline infunction even after repeated impacts.

It is important to note that the key properties of the cell 10 discussedabove are optimized in any particular design in order to deliver theunique Impulse management characteristics also discussed above. If theinitially resistive mechanism of the cell 10, e.g., the collapsible sidewalls 18, is too stiff, the cell 10 will behave similarly to a densefoam; if the initially resistive mechanism (e.g., side walls 18) is toosoft, the cell 10 will behave similarly to a low density foam. If thefluid is not vented from the orifice 16 properly, the cell 10 will notrespond properly after the initial impact. If, for example, the orifice16 is too large, the air does not provide resistance during venting andthe cell 10 behaves similarly to a soft foam; if the orifice 16 is toosmall, the air becomes trapped and behaves like a spring, thus impartingan undesirable bouncing effect as a opposed to a dampening effect.

It is also important to note that not all hollow fluid-filled cavitiesor air chambers will manage energy in this unique manner describedabove. The use of air as an energy management system has been widelyemployed, but in other forms suffers from limitations. Force/Time curvesfor two other types of air-filled cells without any initially resistivemechanism are shown in FIGS. 10 and 11 of the drawings. FIG. 10corresponds to a vented, compressible cell in the form and shape of adisk or flying saucer, with no initially resistive mechanism. FIG. 11corresponds to a vented compressible cell with bellows-like orcorrugated side walls, again with no initially resistive mechanism.

The cells whose Force/Time curves are illustrated in FIGS. 10 and 11fail to provide enough initial resistance to the impact, as evidenced bythe early portions of the curves, which only gradually increase beforethe curve quickly ramps to a high peak force. These curves lookanalogous to those of softer foams. Given the compressibility of air, ifan initial resistive mechanism is not incorporated in the cell, it willcompress too rapidly and fail to yield the rapidly rising, flattenedtrapezoidally shaped curve. Conversely, if the cell is sealed andpressurized, it may become too stiff and not yield enough to manageenergy properly, and may again create an undesirable bouncing effect.Or, if air is contained in an extensive bladder network ofinterconnected compressible cells (as opposed to the relativelycontained environment of the cell 10), upon impact, the air may travelthroughout the bladder and offer very little resistance to impact.

The preferred material, wall thickness, cell geometry and size andorifice size for the cell 10 of FIG. 6 will, of course, depend on theparticular application for which the cell 10 is used, as well as thenumber of such cells used in a particular protective structure and theother elements and components of that structure. As noted, TPE materialsare particularly well suited as the material for the cell 10. Arnitel®and Santoprene™ TPEs are two commercially available TPEs that canreadily be blow-molded to the desired shape and configuration of thecell 10 and that exhibit excellent resiliency and durability. Othermaterials that can be used for the cell 10 include thermoplasticpolyurethane elastomers (TPUs) and low density polyethylene (LDPE).

FIG. 12 of the drawings is a schematic illustration showing across-section and geometric and dimensional details of a preferred cell10 embodied in accordance with the invention. The preferred cellcross-section is represented by the bolder or thicker lines in FIG. 12.The cell 10 of FIG. 12 is preferably symmetrical about its central axisX so that any cross-section of the cell 10 along a plane normal to theaxis X forms a circle. As noted above, this helps assure that theresponse of the cell 10 is the same regardless of the location and angleof the impact. When the cell 10 is cross-sectioned in side elevation atany diameter, such as shown, for example, in FIG. 12, the edges of thecell form a symmetrical shape that passes through a specific set ofpoints arranged in a specific pattern. These points, which may becircles in the case where the edges of the cell 10 are rounded, arelabeled A, A′, B, B′, C, and C′ in FIG. 12. In the pattern, the points Band B′ are equidistant between A and C and A′ and C′, respectively. Theangle formed by the lines AC and AB is greater than zero and less than45°. The same is true of the angles formed by the lines CA and CB, A′C′and A′B′ and C′A′ and C′B′, respectively. Accordingly, the lines AB andBC define an obtuse included angle as do lines A′B′ and B′C′. Other cellcross-sectional shapes that satisfy this definition, and that arepotentially suitable for use for the cell 10 in accordance with theinvention, are represented by the lighter, thinner lines in FIG. 12.

FIG. 13 illustrates other cross-sectional shapes that are potentiallysuitable for use for the cell 10 in accordance with the invention.

As noted above, the specific shape and dimensions of the cell 10 willdepend to some extent on the particular application to which it is put.A cell like cell 10 of FIG. 12 that is intended for use in a protectivestructure, such as that illustrated in, and described below inconnection with, FIG. 17 of the drawings, along with a plurality ofidentical cells 10, shaped and configured for use as protective headgearmay have the following dimensional and other details. The height h ofthe cell 10 of FIG. 12 is about 1.0 inch, the diameters d₁ of its topand bottom walls are about 1.75 inches, and its medial diameter d₂ isabout 2.00 inches. The material of the cell 10 is Arnitel® TPE. The wallthickness t of the cell enclosure 12 may be in the range of about 1.0 toabout 3.00 mm, with a typical thickness (t) of about 2.00 mm. Thediameter of the orifice 16 (see FIG. 6) may be in the range of about 1.0mm to about 5.00 mm, with a typical orifice diameter being about 2.5 mm.It will be appreciated that a variation in any one of these dimensionsand/or angles may require a corresponding adjustment of the otherdimensions and/or angles since all values are interrelated. The optimumcombination of values for a given application may be readily determinedthrough sample testing without undue experimentation.

FIG. 14 shows an alternative embodiment of the invention in the form ofa compressible cell 50 which is similar in design to the cell 10described previously. However, in the cell 50, the initially resistivemechanism is provided by a component that is separate from the enclosure52 of the cell 50 but that coacts with the enclosure 52 to provide thedesired initial resistance. In this illustrative embodiment, theinitially resistive component comprises a resilient plastic ring 62 thatis positioned within the cell 50's enclosure 52. The cell 50 hasgenerally vertical side walls 58 that can be relatively compliant sothat they provide little resistance to collapse in response to animpact. The internal ring 62, however, is designed to resist collapseduring the initial phase of an impact, much the same way that the sidewalls 18 in the cell 10 do, and then strategically buckle inwardly andcollapse, allowing the fluid venting through the orifice 56 of the cell50 serve as the mechanism for handling the remainder of the impact Likethe cell 10, the properties of the cell 50 and its internal ring 62 canbe engineering to yield a nearly trapezoidal, flattened Force/Time curvein response to a wide range of impact energies.

The ring 62 may be fabricated separately from the enclosure 52 of thecell 50 and inserted inside the cell enclosure 52 before the bottom wall54 is secured. The ring 62 may be bonded at its top and bottom edges tothe inside surfaces of the enclosure 52. It will be appreciated that theinitially resistive component could also be disposed outside of the cellenclosure 52 around the perimeter of the cell 50.

FIG. 15 shows another embodiment of the invention in which acompressible cell, such as cell 10 of FIG. 6, is combined with a baseplate 70 of conventional foam. The foam base plate 70 may be bonded orotherwise secured to the cell 10 and may have a central aperture 72which allows fluid to flow freely out of the cell 10 during an impactand back into the cell 10 at the end of the impact. The foam base plate70 improves the combined cell 10's ability to attenuate and absorbimpacts and improves the durability of the cell 10, i.e., its ability towithstand multiple impacts with minimal damage and degradation of itsperformance.

FIG. 16 illustrates still another embodiment to the invention, in whicha protective structure 100 includes a pair of compressible cells, suchas cell 10 of FIG. 6 or cell 50 of FIG. 14, joined to opposite sides ofa common base plate 102. The upper cell 10 or 50 is oriented so that itvents downwardly on impact. The lower cell 10 or 50 is oriented so thatit vents upwardly on impact. The base plate 102, which may be of foam orother plastic, is provided with several counter-extending, radialpassageways 104 which allow fluid to vent laterally from the cells 10 or50 upon impact and to return laterally to the cells 10 or 50 afterimpact. Although the cells 10 or 50 in FIG. 16 are shown to be of thesame relative size, it will be appreciated that they could be ofdifferent sizes, e.g., the lower cell 10 or 50 could be smaller than theupper cell 10 or 50, to conserve space and to make the structure lessbulky.

FIG. 17 is a cross-sectional view of an embodiment of a multilayerprotective shell structure 200 for protecting a body B from damage dueto impacts. The protective structure 200 comprises a plurality ofcompressible cells, such as cell 10 of FIG. 6 or cell 50 of FIG. 14,arranged side-by-side in a middle layer 202 between an outer shell 204and an inner layer 206. The outer shell 204 may be a relatively thin,relatively hard plastic layer that deforms locally and radially inresponse to an impact. The inner layer 206 may be of a conventionalfoam. The cells 10 or 50 may be bonded to the inside surface of theouter shell 204 and/or to the outside surface of the inner layer 206, orsemi-permanently secured thereto by releasable fasteners (not shown).The inner layer 206, like the foam base plate 70 in the embodiment ofFIG. 15, may be provided with a plurality of apertures 208 which allowfluid that vents from the cells 10 or 50 to pass through the inner layer206 to the body B during an impact. It will be appreciated that, becauseof the resilient nature of the cells 10 or 50, the outer shell 204 willnot only deform in response to radial components of an impact, whichcomponents will be effectively absorbed by the cells 10 or 50 and innerlayer 206, but also will shear relative to the inner layer 106 inresponse to tangential components of an impact, absorbing thosecomponents as well.

The layered structure 200 of FIG. 17 is particularly suited for use inthe construction of protective headgear to protect the head of a wearerfrom impact-related concussions and other injury. Specificconfigurations and implementations of the layered structure 200 includesafety helmets, motorcycle helmets, bicycle helmets, ski helmets,lacrosse helmets, hockey helmets, football helmets, batting helmets,headgear for rock or mountain climbing and headgear for boxers. Otherapplications include helmets used on construction sites, in defense andmilitary applications, and for underground activities.

Refer now to FIG. 18 which illustrates another cell embodiment 220 whichis similar to the cell 10 depicted in FIG. 12 except that itsback-to-back frustoconical side walls 222 a and 222 b extending betweenparallel top and bottom walls 224 and 226 are inverted. In other words,walls 222 a, 222 b toe in toward the cell axis, meeting at the medialplane of the cell. In this case, the obtuse included angle defined bylines AB and BC (and lines A′B′ and B′C′) is an exterior included angle.Thus, when the cell 220 collapses, the side walls 222 a, 222 b moveinward toward the cell axis, thereby reducing the volume of the cell andfurther compressing the air therein. Accordingly, cell 220 has asomewhat higher resistance to collapse during the initial phase of animpact than the cell 10 in FIG. 12 whose obtuse included angle is aninterior angle and whose side walls collapse outwardly. The cell 200also has a resilient pad structure secured to the cell wall or baseplate226.

It will also be appreciated that the cells 10, 50 and 220, as well asthe layered structure 200, may be adapted for use in a wide variety ofother impact-absorbing and shock-attenuating applications.

In summary, what we have described is a compressible cell 10, 50 or 220that possesses a unique combination of elements and properties that canbe individually selected and adjusted and that act in coordination withone another to manage impact energy in a novel manner. Specifically, thecells provide the following benefits:

(a) multiple customization options;

(b) phased resistance offered by different impact-absorbing mechanisms(allows shaping of force curve and reduction in peak force);

(c) increased “ride-down” and avoidance of increasing density withcompression (leads to flattening of force curves and reduction in peakforces without the need for increased thickness);

(d) adaptation to varying impact energy levels; and

(e) superior durability compared to foam.

While the invention has been shown and described with reference tospecific embodiments, it will be understood by the skilled in the artthat various modification and additions may be made to the describedembodiments without departing from the scope of the invention as definedby the appended claims. For example, it will be appreciated that thecells may be provided with more than one orifice and that the location,size and configuration of the orifices may vary. Specifically, aseparate orifice with a one-way valve may be provided through which airflows to refill the cell after an impact. In such a case, the outfloworifice or orifices can be relatively small or in the form of slits, sothat they provide optimum resistance to an impact, while the infloworifice or orifices may be relatively large to allow rapid refill of thecell after the impact. Those skilled in the art will also appreciatethat numerous other mechanisms may be devised and used to provide thecell with the desired resistance to collapse during the initial phase ofthe impact. It is thus the intent of the appended claims to cover theseand other modifications that may be made by those skilled in the art.

1. An impact energy management method for protecting a body from damagedue to impacts imparted thereto, the method comprising the steps of:placing a protective structure over at least a portion of the body to beprotected, the protective structure being capable of reducing forces ofan impact that are transferred to the body through the protectivestructure; providing the protective structure with a firstimpact-absorbing mechanism that resists yielding in response to aninitial phase of the impact and that yields to the impact after theinitial phase of the impact; and providing the protective structure witha second impact-absorbing mechanism that attenuates the forces of theimpact after its initial phase such that the forces that are transferredto the body remain substantially constant throughout the remainder ofthe impact.
 2. The method of claim 1 in which the placing step comprisesplacing a protective structure that includes at least onefluid-containing, compressible cell over the portion of the body to beprotected.
 3. The method of claim 2 in which the first impact-absorbingmechanism is provided by providing the cell with side walls designed sothat they resist collapse during the initial phase of the impact andcollapse after the initial impact phase.
 4. The method of claim 2 inwhich the first impact-absorbing mechanism is provided by combining thecell with a component that coacts with the cell to resist collapseduring the initial phase of the impact and to collapse after the initialimpact phase.
 5. The method of claim 4 in which the firstimpact-absorbing mechanism is provided by including a collapsible ringinside the cell that resists collapse during the initial phase of theimpact and that collapses after the initial impact phase.
 6. The methodof claim 2 in which the at least one orifice allows fluid to return tothe cell after the impact.
 7. An impact energy management system forprotecting a body from damage due to impacts imparted thereto, thesystem comprising: a protective structure adapted to be placed over atleast a portion of the body to be protected, said protective structurebeing capable of reducing forces of an impact that are transferred tothe body through said protective structure; a first impact-absorbingmechanism in said protective structure that resists yielding in responseto an initial phase of the impact and that yields to the impact afterthe initial phase of the impact; and a second impact-absorbing mechanismin said protective structure that attenuates the forces of the impactafter its initial phase such that the forces that are transferred to thebody remain substantially constant throughout the remainder of theimpact.
 8. The system of claim 7 in which said protective structurecomprises at least one fluid-containing, compressible cell.
 9. Thesystem of claim 8 in which said first impact-absorbing mechanismcomprises side walls on said cell that are oriented and configured sothat they resist collapse during the initial phase of the impact andthat collapse after the initial impact phase.
 10. The system of claim 8in which said first impact-absorbing mechanism comprises a componentthat coacts with said cell to resist collapse during the initial phaseof the impact and to collapse after the initial impact phase.
 11. Thesystem of claim 10 in which said first impact-absorbing mechanismcomprises a collapsible ring inside said cell that resists collapseduring the initial phase of the impact and that collapses after theinitial impact phase.
 12. The system of claim 8 in which said cell has asubstantially symmetrical shape.
 13. The system of claim 8 in which theat least one orifice allows fluid to return to the cell after theimpact.
 14. A protective structure for protecting a body from impactcomprising: at least one thin-walled enclosure having an uncompressedconfiguration which defines a hollow inner chamber; a volume of fluid atleast partially filling said inner chamber; at least one orifice throughsaid enclosure that resistively vents fluid from the inner chamber inresponse to an impact on said enclosure; an impact-absorbing mechanismassociated with said enclosure that resists yielding in response to aninitial phase of the impact on said enclosure and that yields to theimpact after the initial phase of the impact to allow the remainder ofthe impact to be managed by the fluid venting from said at least oneorifice.
 15. The protective structure of claim 16 in which saidimpact-absorbing mechanism comprises side walls on said enclosure thatare oriented and configured so that they resist collapse during theinitial phase of the impact and that collapse after the initial impactphase.
 16. The protective structure of claim 14 in which said enclosureand said at least one orifice through said enclosure are sized andconfigured so that forces transferred through said structure remainsubstantially constant after the initial phase of the impact.
 17. Theprotective structure of claim 14 in which said at least one orificepermits an inflow of fluid into the inner chamber of said enclosure toreturn said enclosure to its uncompressed configuration after theimpact.
 18. The protective structure of claim 14 in which said enclosurehas a substantially symmetrical shape.
 19. The protective structure ofclaim 14 further including a body of foam joined to said enclosure. 20.The protective structure of claim 14 in which said enclosure is joinedto a second substantially similar enclosure.
 21. The protectivestructure of claim 14 comprising a plurality of said enclosures arrangedside-by-side in a layer and at least one additional layer joined tocorresponding parts of said enclosures.
 22. The protective structure ofclaim 21 wherein said plurality of enclosures is disposed between saidat least one additional layer and a second layer.
 23. The protectivestructure of claim 14 in which said enclosure has a disk shape withcircular top and bottom surfaces of diameter d₁.
 24. The protectivestructure of claim 23 in which said enclosure includes a first side wallportion extending from said top surface and a second side wall portionextending from said bottom surface, said first and second side wallportions joining at a medial plane through said enclosure of diameter d₂which is greater than d₁.
 25. The protective structure of claim 24 inwhich said first and second side wall portions of said enclosure aresubstantially straight in cross section.
 26. The protective structure ofclaim 25 in which said first side wall portion extends at an angle fromsaid top surface, and said second side wall portion extends atsubstantially the same angle from said bottom surface, said angle beinggreater than zero degrees and less than 45 degrees.
 27. The protectivestructure of claim 24 in which said enclosure is formed of athermoplastic elastomer material having a wall thickness in the range ofabout 1.00 millimeter to about 3 millimeters.
 28. The protectiveenclosure of claim 24 further including at least one orifice through oneof said top and bottom surfaces of said enclosure.
 29. The protectiveenclosure of claim 28 in which said at least one orifice has a diameterin the range of about 1.00 millimeter to about 5.00 millimeters.
 30. Theprotective structure of claim 14 in which said enclosure has generallyparallel top and bottom walls and is symmetrical about a central axispassing through said enclosure normal to said top and bottom walls. 31.The protective structure of claim 30 in which said enclosure issymmetrical about a medial plane parallel to said top and bottom walls.32. The protective structure of claim 30 in which said enclosure furtherincludes a first side wall portion extending from said top wall and asecond side wall portion extending from said bottom wall, said first andsecond side wall portions joining at the medial plane.
 33. Theprotective structure of claim 32 wherein said walls of said enclosure,in side cross section, pass through spaced points A, B, C, A′, B′, C′,said points being in a pattern such that a line between A and A′ is in aplane corresponding to said top wall, a line between C and C′ is in aplane corresponding to said bottom wall, and a line between B and B′ isin a medial plane parallel to said top wall and said bottom wall. 34.The protective structure of claim 33 in which the points B and B′ insaid pattern are equidistant between the points A and C and A′ and C′,respectively.
 35. An impact energy management method for protecting abody from damage due to impacts imparted thereto, the method comprisingthe steps of: placing a protective covering over at least one portion ofthe body to be protected, the protective covering being capable ofreducing forces of an impact in accordance with a force/time curve, andproviding the protective covering with an impact-absorbing structurethat resists yielding in response to an initial phase of the impact sothat said curve has a relatively steep leading edge which rises to amaximum force value determined by the impact and then attenuates theforces of the impact after said maximum force value is reached such thatsaid curve thereafter remains substantially constant throughout theremainder of the impact.
 36. An impact management system for protectinga body from damage due to impacts imparted thereto, the systemcomprising: a protective covering adapted to be placed over at least aportion of the body to be protected, said protective covering beingcapable of reducing forces of an impact in accordance with a force/timecurve, and an impact-absorbing structure in said protective coveringthat resist yielding in response to an initial phase of the impact sothat said curve has a relatively steep leading edge which rises to amaximum force value determined by the impact, and then attenuates theforces of the impact after said maximum force value is reached such thatsaid curve thereafter remains substantially constant throughout theremainder of the impact.
 37. The system defined in claim 36 wherein saidimpact-absorbing structure comprises at least one fluid-containingcompressible cell with side walls arranged and adapted to resistcollapse during the said initial phase of the impact and to collapseafter said initial impact phase.
 38. A protective structure forprotecting a body from impact comprising a thin-walled enclosure havingan uncompressed configuration which defines a hollow inner chamber, saidenclosure including a single pair of substantially frustoconical sidewalls connected back to back so as to define an obtuse included anglebetween them, an end wall closing one end of the enclosure, and a baseplate closing the other end of the enclosure.
 39. The protectivestructure of claim 38 wherein the base plate comprises a plastic wall.40. The protective structure of claim 38 wherein the base plate includesan exterior resilient pad.
 41. The protective structure of claim 38wherein the base plate includes a connection surface for connecting theenclosure to a support surface.
 42. The protective structure of claim 38wherein the obtuse included angle is an interior included angle.
 43. Theprotective structure of claim 28 wherein the obtuse included angle is anexterior included angle.